1. Field of the Invention
The invention relates to a process for preparing carbamatoorganosilanes from corresponding aminoorganosilanes and dialkyl carbonate.
2. Description of the Related Art
Various processes for preparing 3-carbamatopropylsilanes of the formula (1) are known from the prior art.

Preparative processes customarily employed usually start out from 3-aminopropylsilanes of the formula (2) and these are reacted with dialkyl carbonates with elimination of an alcohol to form the product. Said processes are described, for example, in EP 0 583 581, U.S. Pat. No. 6,673,954 or WO 2007/037817.

However, the processes as described in the prior art have a number of disadvantages. Firstly, comparatively large amounts (>0.25%) of a basic metal alkoxide are used as catalyst. These have to be neutralized before the crude product mixture is worked up, and the metal salts formed here make an additional filtration step necessary. It would therefore be desirable to reduce the amount of catalyst to a minimum, ideally to such an extent that, in an industrial process, it is sufficient to drain off the fully worked up product mixture through a simple filter unit in the reactor outlet. Such “police filters”, which remove very small amounts of possible suspended materials from a reaction product, are prior art and are present in most industrial production plants.
A further disadvantage of the processes described in the prior art lies in either moderate yields of 78-92% (U.S. Pat. No. 6,673,954) or relatively large amounts (about 2%) of unreacted aminosilanes (EP 0 583 581). Here, unreacted aminosilanes, in particular, represent a great problem since firstly they can be removed only with difficulty from the product and secondly they react, in the most important application of carbamatosilanes, viz. use for the synthesis of the corresponding isocyanatosilanes, with the latter, which leads to urea by-products, biuret by-products or even oligomeric or polymeric by-products.
It would therefore be desirable to have a process which no longer has these disadvantages.